SampleSystem2.cs

using Unity.Entities;
using Unity.Transforms;

public class SampleSystem2 : ComponentSystem
{
    ComponentGroup _group;

    protected override void OnCreateManager()
    {
        _group = GetComponentGroup(
            ComponentType.Create<Position>(), 
            ComponentType.Create<Box>(), 
            ComponentType.Create<Score>());
    }

    protected override void OnUpdate()
    {
        Entities.With(_group).ForEach((ref Position pos, ref Box box) => {
            // do somethings
        }); // Groupを登録

        Entities.With(_group).ForEach((ref Position pos, ref Score score) => {
            // do somethings
        }); // Groupを登録
    }
}